SECONDARY SEXUAL CHARACTERS 121 



sexual characters of the male, while the sex glands of the 

 female suppress these characters. 



Wallace's theory leaves out of account the hereditary 

 factor that is also present and which acts quite apart 

 from the physiological effects of the sex glands. 



Cunningham, who has more recently written on the 

 same subject, accepts the hormone hypothesis as the 

 basis for all cases of secondary sexual characters. 

 But he fails to make good his view when it is applied 

 to insects, for.reasons that we shall take up later. He is 

 especially concerned, however, in the attempt to make 

 plausible his own hypothesis that secondary sexual 

 characters have arisen through the use of the parts, or 

 through special nervous or blood suppHes to certain lo- 

 cahties of the body which become suffused during sexual 

 excitement. In both cases he thinks the increased local 

 activity will cause the cells to produce hormones that 

 will be dispersed throughout the body, and absorbed 

 by other cells. The germ-cells will in this way get 

 their share and carry over the hormone to the next 

 generation. 



Cunningham forgets one important point. If these 

 imaginary hormones can get out of cells and into germ- 

 cells, they can get out of the germ-cells again. Hence 

 in the long period of embryonic and juvenile existence 

 through which the individual passes before the second- 

 ary sexual characters appear they would surely be lost 

 from the body like any other ordinary hormone. 



CONTINUOUS VARIATION AS A BASIS FOR SELECTION 



And now let us turn to an entirely different aspect of 

 the matter. What could selection do, admitting that 

 selection may take place. For fifty years it has been 



